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1.
Dalton Trans ; 2020 Apr 03.
Artigo em Inglês | MEDLINE | ID: mdl-32242884

RESUMO

The coordination characteristics and donor/acceptor properties of a series of 2-pyridyl substituted phosphine ligands have been investigated using structural, spectroscopic and DFT calculational studies. A range of different coordination modes are observed in Mo and W carbonyl complexes of tris-2-pyridyl-phosphine ligands of the type P(2-py') (2-py' = substituted or unsubstituted 2-pyridyl group), including an unprecedented example exhibiting N,N',µ2-π coordination. DFT calculations were used to assess the relative donor/acceptor properties of a range of related 2-pyridyl-phosphine ligands with respect to PPh3 and PtBu3.

2.
Dalton Trans ; 48(39): 14724-14736, 2019 Oct 07.
Artigo em Inglês | MEDLINE | ID: mdl-31538996

RESUMO

The σ-amine-borane pincer complex [Rh(PONOP)(η1-H3B·NMe3)][BArF4] [2, PONOP = κ3-NC5H3-2,6-(OPtBu2)2] is prepared by addition of H3B·NMe3 to the dihydrogen precursor [Rh(PONOP)(η2-H2)][BArF4], 1. In a similar way the related H3B·NMe2H complex [Rh(PONOP)(η1-H3B·NMe2H)][BArF4], 3, can be made in situ, but this undergoes dehydrocoupling to reform 1 and give the aminoborane dimer [H2BNMe2]2. NMR studies on this system reveal an intermediate neutral hydride forms, Rh(PONOP)H, 4, that has been prepared independently. 1 is a competent catalyst (2 mol%, ∼30 min) for the dehydrocoupling of H3B·Me2H. Kinetic, mechanistic and computational studies point to the role of NMe2H in both forming the neutral hydride, via deprotonation of a σ-amine-borane complex and formation of aminoborane, and closing the catalytic cycle by reprotonation of the hydride by the thus-formed dimethyl ammonium [NMe2H2]+. Competitive processes involving the generation of boronium [H2B(NMe2H)2]+ are also discussed, but shown to be higher in energy. Off-cycle adducts between [NMe2H2]+ or [H2B(NMe2H)2]+ and amine-boranes are also discussed that act to modify the kinetics of dehydrocoupling.

3.
Chemistry ; 25(61): 14003-14009, 2019 Nov 04.
Artigo em Inglês | MEDLINE | ID: mdl-31469199

RESUMO

The systematic assembly of supramolecular arrangements is a persistent challenge in modern coordination chemistry, especially where further aspects of complexity are concerned, as in the case of large molecular mixed-metal arrangements. One targeted approach to such heterometallic complexes is to engineer metal-based donor ligands of the correct geometry to build 3D arrangements upon coordination to other metals. This simple idea has, however, only rarely been applied to main group metal-based ligand systems. Here, we show that the new, bench-stable tris(3-pyridyl)stannane ligand PhSn(3-Py)3 (3-Py=3-pyridyl) provides simple access to a range of heterometallic SnIV /transition metal complexes, and that the presence of weakly coordinating counter anions can be used to build discrete molecular arrangements involving anion encapsulation. This work therefore provides a building strategy in this area, which parallels that of supramolecular transition metal chemistry.


Assuntos
Complexos de Coordenação/química , Metais/química , Polímeros/química , Compostos de Estanho/química , Cristalografia por Raios X , Ligantes , Conformação Molecular , Estanho/química
4.
Dalton Trans ; 48(28): 10628-10641, 2019 Jul 16.
Artigo em Inglês | MEDLINE | ID: mdl-31231728

RESUMO

Sequential treatment of [W([triple bond, length as m-dash]CBr)(CO)2(Tp*)] (Tp* = hydrotris(dimethylpyrazolyl)borate) with nBuLi and Cl2PNiPr2 provides the aminochlorophosphinocarbyne [W([triple bond, length as m-dash]CPClNiPr2)(CO)2(Tp*)]. The chloro substituent undergoes subsitution with RLi (R = Me, Et, Ph) to afford [W([triple bond, length as m-dash]CPRNiPr2)(CO)2(Tp*)] and with [W([triple bond, length as m-dash]CLi)(CO)2(Tp*)] to give the aminobis(alkylidynyl)phosphine [iPr2NP{C[triple bond, length as m-dash]W(CO)2(Tp*)}2]. Treatment with Li[BHEt3] gives the primary aminophosphine [W([triple bond, length as m-dash]CPHNiPr2)(CO)2(Tp*)], formed in a mixture with the ethyl derivative [W([triple bond, length as m-dash]CPEtNiPr2)(CO)2(Tp*)]. Although they could not be isolated, spectroscopic data indicated that halide abstraction with Al2Cl6 forms the phosphaisonitrile salt [W(CPNiPr2)(CO)2(Tp*)][AlCl4], which displays electrophilic character at phosphorus, e.g., in the reaction with diphenylacetylene to furnish the phosphirenium salt [W{CP(C2Ph2)NiPr2}(CO)2(Tp*)][AlCl4]. Finally, the reaction with LiNPh2 gives the mixed diaminophosphinocarbyne, [W{[triple bond, length as m-dash]CP(NiPr2)(NPh2)}(CO)2(Tp*)].

5.
Dalton Trans ; 48(17): 5692-5697, 2019 Apr 23.
Artigo em Inglês | MEDLINE | ID: mdl-30968911

RESUMO

Post-functionalisation of the aluminate anion [EtAl(6-R-2-py)3]- (6-R-2-py = 6-R-2-pyridyl, R = Me or Br) can be accomplished via nucleophilic addition of the pyridyl groups to the electrophilic C[double bond, length as m-dash]O group of aldehydes (RCH[double bond, length as m-dash]O) or by deprotonation of carboxylic acids (RCO2H). NMR spectroscopic and crystallographic studies show how 6-Me-2-py groups can detect chirality and reveal a new aspect of isomerism.

6.
Chemistry ; 25(6): 1379-1390, 2019 Jan 28.
Artigo em Inglês | MEDLINE | ID: mdl-30338876

RESUMO

The dehydropolymerization of amine-boranes, exemplified as H2 RB⋅NR'H2 , to produce polyaminoboranes (HRBNR'H)n that are inorganic analogues of polyolefins with alternating main-chain B-N units, is an area with significant potential, stemming from both fundamental (mechanism, catalyst development, main-group hetero-cross-coupling) and technological (new polymeric materials) opportunities. This Concept article outlines recent advances in the field, covering catalyst development and performance, current mechanistic models, and alternative non-catalytic routes for polymer production. The substrate scope, polymer properties and applications of these exciting materials are also outlined. Challenges and opportunities in the field are suggested, as a way of providing focus for future investigations.

7.
Dalton Trans ; 47(20): 7036-7043, 2018 May 22.
Artigo em Inglês | MEDLINE | ID: mdl-29741181

RESUMO

Difficulties in the preparation of neutral ligands of the type [RSi(2-py)3] (where 2-py is an unfunctionalised 2-pyridyl ring unit) have thwarted efforts to expand the coordination chemistry of ligands of this type. However, simply switching the pyridyl substituents to 6-methyl-pyridyl groups (6-Me-2-py) in the current paper has allowed smooth, high-yielding access to the [PhSi(6-Me-2-py)3] ligand (1), and the first exploration of its coordination chemistry with transition metals. The synthesis, single-crystal X-ray structures and solution dynamics of the new complexes [{PhSi(6-Me-2-py)3}CuCH3CN][PF6], [{PhSi(6-Me-2-py)3}CuCH3CN][CuCl2], [{PhSi(6-Me-2-py)3}FeCl2], [{PhSi(6-Me-2-py)3}Mo(CO)3] and [{PhSi(6-Me-2-py)3}CoCl2] are reported. The paramagnetic Fe2+ and Co2+ complexes show strongly shifted NMR resonances for the coordinated pyridyl units due to large Fermi-contact shifts. However, magnetic anisotropy also leads to considerable pseudo-contact shifts so that both contributions have to be included in the paramagnetic NMR analysis.

8.
Angew Chem Int Ed Engl ; 57(22): 6648-6652, 2018 05 28.
Artigo em Inglês | MEDLINE | ID: mdl-29603844

RESUMO

Although a multitude of studies have explored the coordination chemistry of classical tripodal ligands containing a range of main-group bridgehead atoms or groups, it is not clear how periodic trends affect ligand character and reactivity within a single ligand family. A case in point is the extensive family of neutral tris-2-pyridyl ligands E(2-py)3 (E=C-R, N, P), which are closely related to archetypal tris-pyrazolyl borates. With the 6-methyl substituted ligands E(6-Me-2-py)3 (E=As, Sb, Bi) in hand, the effects of bridgehead modification alone on descending a single group in the periodic table were assessed. The primary influence on coordination behaviour is the increasing Lewis acidity (electropositivity) of the bridgehead atom as Group 15 is descended, which not only modulates the electron density on the pyridyl donor groups but also introduces the potential for anion selective coordination behaviour.

9.
Chemistry ; 24(53): 14127-14136, 2018 Sep 20.
Artigo em Inglês | MEDLINE | ID: mdl-29573487

RESUMO

In an attempt to prepare new Fe catalysts for the dehydrocoupling of amine-boranes and to provide mechanistic insight, the paramagnetic FeII dimeric complex [Cp'FeI]2 (1) (Cp'=η5 -((1,2,4-tBu)3 C5 H2 )) was used as a precursor to a series of cyclopentadienyl FeII and FeIII mononuclear species. The complexes prepared were [Cp'Fe(η6 -Tol)][Cp'FeI2 ] (2) (Tol=C6 H5 Me), [Cp'Fe(η6 -Tol)][BArF4 ] (3) (BArF4 =[B(C6 H3 (m-CF3 )2 )4 ]- ), [N(nBu)4 ][Cp'FeI2 ] (4), Cp'FeI2 (5), and [Cp'Fe(MeCN)3 ][BArF4 ] (6). The electronic structure of the [Cp'FeI2 ]- anion in 2 and 4 was investigated by SQUID magnetometry, EPR spectroscopy and ab initio Complete Active Space Self Consistent Field-Spin Orbit (CASSCF-SO) calculations, and the studies revealed a strongly anisotropic S=2 ground state. Complexes 1-6 were investigated as catalysts for the dehydrocoupling of Me2 NH⋅BH3 (I) in THF at 20 °C to yield the cyclodiborazane product [Me2 N-BH2 ]2 (IV). Complexes 1-4 and 6 were active dehydrocoupling catalysts towards I (5 mol % loading), however 5 was inactive, and ultra-violet (UV) irradiation was required for the reaction mediated by 3. Complex 6 was found to be the most active precatalyst, reaching 80 % conversion to IV after 19 h at 22 °C. Dehydrocoupling of I by 1-4 proceeded via formation of the aminoborane Me2 N=BH2 (II) as the major intermediate, whereas for 6 the linear diborazane Me2 NH-BH2 -NMe2 -BH3 (III) could be detected, together with trace amounts of II. Reactions of 1 and 6 with Me3 N⋅BH3 were investigated in an attempt to identify Fe-based intermediates in the catalytic reactions. The σ-complex [Cp'Fe(MeCN)(κ2 -H2 BH⋅NMe2 H][BArF4 ] was proposed to initially form in dehydrocoupling reactions involving 6 based on ESI-MS (ESI=Electrospray Ionisation Mass Spectroscopy) and NMR spectroscopic evidence. The latter also suggests that these complexes function as precursors to iron hydrides which may be the true catalytic species.

10.
Chemistry ; 24(21): 5450-5455, 2018 Apr 11.
Artigo em Inglês | MEDLINE | ID: mdl-29504649

RESUMO

The rhodium complex [Rh(Ph2 PCH2 CH2 CH2 PPh2 )(η6 -FC6 H5 )][BArF4 ], 2, catalyzes BH/BD exchange between D2 and the boranes H3 B⋅NMe3 , H3 B⋅SMe2 and HBpin, facilitating the expedient isolation of a variety of deuterated analogues in high isotopic purities, and in particular the isotopologues of N-methylamine-borane: R3 B⋅NMeR2 1-dx (R=H, D; x=0, 2, 3 or 5). It also acts to catalyze the dehydropolymerization of 1-dx to give deuterated polyaminoboranes. Mechanistic studies suggest a metal-based polymerization involving an unusual hybrid coordination insertion chain-growth/step-growth mechanism.

11.
J Am Chem Soc ; 140(4): 1481-1495, 2018 01 31.
Artigo em Inglês | MEDLINE | ID: mdl-29286647

RESUMO

A systematic study of the catalyst structure and overall charge for the dehydropolymerization of H3B·NMeH2 to form N-methyl polyaminoborane is reported using catalysts based upon neutral and cationic {Rh(Xantphos-R)} fragments in which PR2 groups are selected from Et, iPr, and tBu. The most efficient systems are based upon {Rh(Xantphos-iPr)}, i.e., [Rh(κ3-P,O,P-Xantphos-iPr)(H)2(η1-H3B·NMe3)][BArF4], 6, and Rh(κ3-P,O,P-Xantphos-iPr)H, 11. While H2 evolution kinetics show both are fast catalysts (ToF ≈ 1500 h-1) and polymer growth kinetics for dehydropolymerization suggest a classical chain growth process for both, neutral 11 (Mn = 28 000 g mol-1, D = 1.9) promotes significantly higher degrees of polymerization than cationic 6 (Mn = 9000 g mol-1, D = 2.9). For 6 isotopic labeling studies suggest a rate-determining NH activation, while speciation studies, coupled with DFT calculations, show the formation of a dimetalloborylene [{Rh(κ3-P,O,P-Xantphos-iPr)}2B]+ as the, likely dormant, end product of catalysis. A dual mechanism is proposed for dehydropolymerization in which neutral hydrides (formed by hydride transfer in cationic 6 to form a boronium coproduct) are the active catalysts for dehydrogenation to form aminoborane. Contemporaneous chain-growth polymer propagation is suggested to occur on a separate metal center via head-to-tail end chain B-N bond formation of the aminoborane monomer, templated by an aminoborohydride motif on the metal.

12.
Nat Commun ; 8: 15022, 2017 04 07.
Artigo em Inglês | MEDLINE | ID: mdl-28387308

RESUMO

Organoboranes are some of the most synthetically valuable and widely used intermediates in organic and pharmaceutical chemistry. Their synthesis, however, is limited by the behaviour of common boron starting materials as archetypal Lewis acids such that common routes to organoboranes rely on the reactivity of boron as an electrophile. While the realization of convenient sources of nucleophilic boryl anions would open up a wealth of opportunity for the development of new routes to organoboranes, the synthesis of current candidates is generally limited by a need for highly reducing reaction conditions. Here, we report a simple synthesis of a magnesium boryl through the heterolytic activation of the B-B bond of bis(pinacolato)diboron, which is achieved by treatment of an easily generated magnesium diboranate complex with 4-dimethylaminopyridine. The magnesium boryl is shown to act as an unambiguous nucleophile through its reactions with iodomethane, benzophenone and N,N'-di-isopropyl carbodiimide and by density functional theory.

13.
Dalton Trans ; 46(13): 4355-4365, 2017 Mar 27.
Artigo em Inglês | MEDLINE | ID: mdl-28287661

RESUMO

The phosphinocarbyne complex [W([triple bond, length as m-dash]CPPh2)(CO)2(Tp*)] (1: Tp* = hydrotris(dimethylpyrazolyl)borate) coordinates transition metal fragments via the phosphine to form bimetallic species [W{[triple bond, length as m-dash]CPPh2RhCl2(Cp*)}(CO)2(Tp*)] (2) and [W([triple bond, length as m-dash]CPPh2AuCl)(CO)2(Tp*)] (3). Appropriately tailored sterics allow for complexation of a second equivalent of AuCl to afford the trimetallic complex [W{η2-C(AuCl)PPh2AuCl}(CO)2(Tp*)] (4), containing an Au-W-C dimetallacyclopropene connectivity. Similarly, AuCl binds to the carbyne linkage in [W{[triple bond, length as m-dash]CP([double bond, length as m-dash]S)Ph2}(CO)2(Tp*)], yielding [W{η2-C(AuCl)P([double bond, length as m-dash]S)Ph2}(CO)2(Tp*)] (5). In the case of auration of the ditungsten species [W2(µ-C2PPh)(CO)4(Tp*)2] (6), variation in the stoichiometry leads to trimetallic [W2(µ-C2PPhAuCl)(CO)4(Tp*)2] (7) and pentametallic [W2{µ-(η2-CAuCl)2PPhAuCl}(CO)4(Tp*)2] (8) complexes, via a proposed tetrametallic intermediate [W2{µ-(η2-CAuCl)2PPh}(CO)4(Tp*)2], the site selectivity being dictated by aurophilic interactions.

14.
Chem Commun (Camb) ; 53(11): 1832-1835, 2017 Feb 07.
Artigo em Inglês | MEDLINE | ID: mdl-28111645

RESUMO

A range of bis(alkylidynyl)phosphines RP{C[triple bond, length as m-dash]M(CO)2(Tp*)}2 (M = Mo, W; R = Cl, Ph, Cy; Tp* = hydrotris(dimethylpyrazolyl)borate) are obtained from the reactions of [M([triple bond, length as m-dash]CLi)(CO)2(Tp*)] with Cl2PR or alternatively via the palladium(0)-mediated reactions of [W([triple bond, length as m-dash]CBr)(CO)2(Tp*)] with RPH2 (R = Py, Cy). The complexes RP{C[triple bond, length as m-dash]W(CO)2(Tp*)}2 rearrange slowly (R = Cl) or on heating (R = Ph) to afford the isomeric phospha-acyls [W2(µ:η1-C;η2-C,P-CCPR)(CO)4(Tp*)2].

15.
Angew Chem Int Ed Engl ; 54(50): 15280-3, 2015 Dec 07.
Artigo em Inglês | MEDLINE | ID: mdl-26473402

RESUMO

The alkaline-earth element bis(trimethylsilyl)amides, [Ae{N(SiMe3 )2 }2 (thf)2 ] [Ae=Mg, Ca, Sr], are effective precatalysts for boron-nitrogen bond formation through the desilacoupling of amines, RR'NH (R=alkyl, aryl; R'=H, alkyl, aryl), and pinBSiMe2 Ph. This reactivity also yields a stoichiometric quantity of Me2 PhSiH and provides the first example of a catalytic main-group element-element coupling that is not dependent on the concurrent elimination of H2 .

16.
J Am Chem Soc ; 136(50): 17442-5, 2014 Dec 17.
Artigo em Inglês | MEDLINE | ID: mdl-25470387

RESUMO

The palladium-mediated reaction of [W(≡CBr)(CO)2(Tp*)] (Tp* = hydrotris(3,5-dimethylpyrazol-1-yl)borate) with primary phosphines PH2R (R = Ph, Cy) affords the secondary phosphinocarbyne complexes [W(≡CPHR)(CO)2(Tp*)], deprotonation of which provides the anionic phosphaisonitrile complexes [W(CPR)(CO)2(Tp*)](-), including the structurally characterized salt [W(CPPh)(CO)2(Tp*)][K(kryptofix)].

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